Internal combustion engines produce waste heat energy in addition to the mechanical energy generated to propel a vehicle. If the excess heat energy is removed, the engine block could overheat and crack, or otherwise break, necessitating expensive repairs. In many engines, an liquid cooling system removes the unwanted heat by providing a network of passages and conduits in the engine block through which liquid coolant circulates. The coolant then passes through a multi-finned radiator over which ambient air flows, extracting the heat.
Unwanted air can be introduced into the cooling system when it is being filled with coolant, for example, following repairs at a service station. The air may accumulate and form bubbles which can become trapped at various locations in the cooling system even though the coolant level appears to indicate that the cooling system is full. Unless the trapped air is removed, coolant flow can be reduced perhaps causing the engine to overheat, or can cause insufficient heater and defroster performance.
As a precautionary measure following filling of an automotive cooling system, current practice is to run the engine for a period of time to circulate the coolant in the system, with the cooling system fill/pressure cap removed, so that trapped air can escape. This procedure is time consuming, however, and essentially assumes that all trapped air will circulate past the open filler neck and escape after a certain length of time. If the volume of trapped air in the cooling system could be determined, the time an engine would have to be run to expel that air could be more accurately estimated, thus saving time and expense.
One method of determining whether air is trapped in the cooling system is shown in FIG. 7. Cooling system 112 is filled with coolant 114. A radiator 116 is connected to cooling system 112 by hoses 118. An air bubble 120 trapped in the cooling system can be detected, if large enough, when the level 122 of coolant in a pressure vessel 124, which is attached to the radiator filler neck 126, decreases upon pressurization of the air above level 122 by pump 128. However, this method is adversely affected by temperature changes and coolant level in pressure vessel 124. In addition, the device is heavy, bulky, and difficult to set up or to move easily, particularly when used in close quarters under the hood of an engine.